Agricultural vehicles may sometimes have two or more electronic control units (ECU's). For example, there may be an ECU for engine management and others to control an implement or to control some other specific function performed by the vehicle.
Hitherto, ECU's are housed in separate housing modules which were shaped as a rectangular box. The height of the box needs to be sufficient to clear the circuit components mounted on the board, of which the highest is usually a connector which enables a set of wires to be plugged into the board. In the past, other components could also protrude significantly from the circuit board but with more modern circuit boards making use of surface mount technology, the board is itself slim and it is mainly the connectors that dictate the height of the housing.
When conventional housing modules are stacked above one another, the height of the stack is equal to the sum of the heights of the individual modules and the space needed to house the ECU's is considerable.